The present invention relates generally to shrink packaging machines and, in particular, to shrink packaging machines for shrink wrapping thin or lightweight articles including, for example, easily deformed, bent, or folded articles that are thin or light weight, and that have a range of various heights.
In shrink wrapping articles, it is common to entirely cover each article top and bottom with a shrink film, such as polyvinyl chloride or polypropylene soft shrink material, and then transport the article covered in shrink film on a mesh or solid belt conveyer, or sometimes a roller conveyer, through a shrink tunnel including a hot air chamber. Typically, hot air is heated to between 150° Fahrenheit and 600° Fahrenheit and blown in the hot air chamber onto the shrink film while it is conveyed through the shrink tunnel. The hot air shrinks the shrink film about the article.
If the article happens to be thin, then pressure exerted on the article by the shrinking film tends to cause deformation or bending of the article. Additionally, if the article happens to be lightweight, then turbulent air blown within the hot air chamber tends to cause the article to float or otherwise lift off of the conveyor and move around within the chamber, which is undesirable.
A number of approaches to solving the problem of shrink wrapping thin or lightweight articles have been utilized. One older approach utilizes both bottom and top mesh or solid belt conveyers synchronized to travel in the same direction through the tunnel at the same speed. The top conveyer is spaced over the bottom conveyer at a distance which allows the particular article to fit between and contact the two conveyers. The use of two synchronized conveyers is fairly expensive and requires resetting of the distance between the two conveyers whenever an article having a new thickness is to be shrink wrapped. Furthermore, such an approach can not be readily deployed in existing shrink packaging machines that are not built to accommodate this approach.
In another approach to solving the problem of shrink wrapping thin or lightweight articles, efforts have been made to develop a low energy shrink film which can be used at lower temperatures and with less air circulation. Although such an approach may have merit, more traditional mechanical approaches may be preferable.
Another approach developed some years ago is disclosed in U.S. Pat. No. 5,009,057 to Wilkinson (“the '057 Patent”), the entirety of which is hereby incorporated herein by reference. This approach is illustrated and described herein with respect to FIGS. 1-12, and the present invention is considered to represent an improvement to shrink packaging machines and methods that utilize the approach of the '057 Patent.
In accordance with the '057 Patent, a shrink packaging machine 10 represented in FIGS. 1-5 includes a conveyer 12 for transporting an article 46 wrapped in shrink film through a shrink tunnel 14 and a hot air chamber 16 in which hot air is blown onto the shrink film within the shrink tunnel 14. The shrink packaging machine 10 also includes an apparatus 18 that prevents the article from becoming deformed and prevents the article from lifting off of the conveyer 12 during the shrink wrapping process.
The apparatus 18 includes a plurality of spaced apart rollers 20 and a support 22 for disposition of the plurality of rollers 20 above the conveyer 12. The plurality of rollers 20 are maintained by the support 22 in a disposition above and out of contact with the conveyer 12. Alternatively, the rollers 20 may be maintained by the support 22 in a disposition in which the rollers 20 rest upon the conveyer 12 as shown in order to accommodate an extremely thin article 46.
Each of the plurality of rollers 20 includes a central horizontal shaft 24 and a cylinder 26 rotatably mounted on the shaft 24. Each cylinder 26 is covered with a high temperature-resistant non-stick coating, such as silicon rubber or Teflon®. Support 22 includes a pair of side rails 28,30 spaced apart and forming slots 32 for receiving opposite ends of the shafts 24. The slots 32 of the left side rail 28 are directly opposite and identical in shape to corresponding slots 32 of the right side rail 30 so that the axis of each of the plurality of rollers 20 extends in a direction generally orthogonal to the direction of motion 34 of the conveyer 12.
The support 22 also includes threaded studs 36 passing through both side rails 28,30 for securing the side rails 28,30 in a fixed, spaced apart relationship. Each threaded stud 36 is secured to the side rails 28,30 by inner nuts 38 and outer nuts 40.
As shown in FIG. 5, each slot 32 extends in a direction that includes both a vertical component 42 and a horizontal component 44 relative to the direction of the conveyor motion 34. The vertical component 42 allows the vertical displacement of a corresponding one of the plurality of rollers 20 by an article 46 as the article is conveyed past the roller 20. The horizontal component 44 allows a corresponding roller 20 to be pushed slightly backwards in the direction of motion 34 of the conveyer 12, thereby making it easier for the article 46 to lift the roller 20.
As shown in FIG. 3, the support 22 also includes threaded legs 48 mounted to pivot about axes 50 in respective directions 52,54 that are transverse to the direction of motion 34 of the conveyer 12. The legs 48 thus can be pivoted outwardly from the side rails 28,30 and adjusted in length through adjusting nuts 56 to properly brace against side ledges 58 and upwardly extending lips 60 of the shrink packaging machine 10. The threaded legs 48 are of the same diameter and thread pitch as the threaded studs 36 so that all may be cut from the same stock. By simply cutting the threaded studs 36 to the proper length, the apparatus 18 can be easily made to work with any width conveyer or article 46.
Each side rail 28,30 may form regularly spaced upper holes 62 and regularly spaced lower holes 64 positioned just above the slots 32 for receiving the threaded studs 36. The side rails 28,30 also form regularly spaced pairs of apertures 65 for receiving mounts 66 for the mounting of threaded legs 48. The rails 28,30 can thus be cut to any length without special manufacture, and both rails can be cut from the same stock, simply reversing the direction which a particular rail faces to make it either a right side rail 30 or a left side rail 28.
A thin flat article 46 is shrink wrapped by covering the article 46 with shrink film and then conveying the article 46 on conveyer 12 through the shrink tunnel 14. At least one of the plurality of rollers 20 forcibly holds down the article 46 forcing it into constant engagement with the conveyor 12 as hot air is blown on article 46 in the hot air chamber 16. The plurality of spaced apart rollers 20 permits the hot air to be blown in-between the rollers 20 and around the article 46.
In the shrink packaging machine 10 as shown in FIGS. 1-5, the cylinders 26 of the rollers 20 actually contact the surface of the conveyer 12 which, in turn, imparts to each cylinder 26 rotational motion around its respective shaft 24 further facilitating the movement of the article 46 covered in shrink film through the shrink tunnel 14. In this respect, the rollers 20 each at least contacts the particular article 46 during its passage through the shrink tunnel 14 even if each roller 20 does not actually touch the conveyer 12, although it also is possible for the rollers 20 to be disposed just slightly above the article 46 in order to simply prevent the article 46 from curling or deforming more than a limited amount.
A second apparatus 18 representative of the approach of the '057 Patent is illustrated in FIGS. 6-12, wherein similar structures are referenced by the same callout numbers. The illustrations of the second apparatus 18 have been simplified in order to render more apparent the differences between the prior art of the '057 Patent and various embodiments of the present invention.
In this respect, a right side elevational view of the second apparatus is illustrated in FIG. 6, and a front elevational view of the second apparatus 18 is illustrated in FIG. 7. A right side elevational view of the second apparatus 18 is illustrated in FIG. 8 and is shown in operation with a conveyor 12 of a shrink packaging machine 10 wherein a thin article 46 is about to be shrink wrapped. Because of the low profile (height) of the article 46 relative to the diameter of the rollers 20, the article 46 moves smoothly underneath the rollers 20 by displacing them vertically and horizontally. Articles 86 relatively thicker than article 46 also may be guided smoothly underneath the rollers 20 if the thicker articles 86 have appropriate contours that enable each roller 20 to be displaced vertically and horizontally, as shown in FIGS. 9-10. For example, the articles 86 of FIGS. 9-10 each includes a generally wedge-shaped profile on its leading edge that provides an incline for ascension of the rollers 20.
In contrast, the second apparatus 18 of the shrink packaging machine may not properly work with a series of thick, non-contoured articles 146 to be shrink wrapped as illustrated, for example, in FIGS. 11-12. In this scenario, the thicker size of the lead article 146 tends to contact the first roller 20 at an angle nearly perpendicular to the surface of the roller 20 and, instead of being guided smoothly underneath the roller 20, the article 146 is blocked and even damaged by the roller 20, as illustrated in FIG. 12.
In this situation, even though the second apparatus 18 may have sufficient vertical roller movement to accommodate the thickness of the article 146, the thickness of the article 146 relative to the diameter of the roller 20 and the distance between the roller 20 and the conveyor 12 act to prevent such vertical displacement from occurring. This further leads to lifting of the rearward portion of the article 146 off of the conveyor 12, especially when the first roller is disposed in contact with the conveyor 12 and, as a result, is undergoing rotational movement that tends to force downward the front portion of the article 146.
As will be appreciated by the Ordinary Artisan, the scenario illustrated in FIG. 12 may result in damage to the article 146, misalignment of one or more of the articles 146 passing into the second apparatus 18, and/or jamming of the apparatus 18, all of which then may require undesired manual intervention. moreover, it will be appreciated that, while the second apparatus 18 illustrated in FIGS. 11-12 could be raised to properly work with the thicker articles 146, such modification and setup of the shrink packaging machine 10 also requires manual intervention.
Accordingly, a need exists for an apparatus that may be used, for example, in place of the second apparatus of FIGS. 6-12 and that accommodates both the articles 46 and articles 146 shown therein. One or more embodiments of the present invention comprise such an apparatus.